The object of the invention hereinafter described is a valve incorporated in the capping film of a package, which permits the vapours evolved during heating of the contents to escape without permitting the heating medium (usually water) to penetrate the contents.
Expansion of the liquid contents and evaporation of the aqueous constituents when the contents of a ready-to-serve meal packed in a semi-solid dish, for example, are heated results in the production of an overpressure which causes hot liquid fragments of the contents to spurt out when the package is opened. This fact may impose a restriction on the use of otherwise suitable ready-to-serve dishes.
The invention described hereinafter resolves the problem by incorporation of a valve in the capping film, which is only exposed immediately prior to heating of the contents of the package.